Electrical measuring apparatus



Jan. 12 1926'.

A. B. CLARK ET AL "ELECTRICAL MEASURING APPARATUS Filed Dec. 22, 1923 2 Shanta-Sheet 2 .4- fimstaw m miles lad/20ml 10ml byymss. B= Clasps-Mk with load yymuzs'.

' IN VEN TORS Jffi Chi/k WU. @2560! A 'ITOIENE Y Patented Jan. 12, 1926.

UNIT Ensures PATENT OFFICE.

ALVA BENSON CLARK, OF BROOKLYN, NEW YORK, AND GEORGE CRISSON, OF HACKEN- SACK, NEW JERSEY, ASSIGNORS TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

ELECTRICAL MEASURING APPARATUS.

Application filed December 22, 1923. Serial No. 682,267.

To all whom it may concern:

Be it known that we, ALVA BENSON CLARK and Gnonon Caisson, citizens of the United States, residing at Brooklyn and Hackensack, in the counties of Kings and Bergen and States of New York and New Jersey, respectively, have invented certain Improve ments in Electrical Measuring Apparatus, of which the following is a specification.

This invention relates to electrical measuringapparatus and particularly to means for locatingthe cause of crosstalk between adjacent signaling circuits.

It is well known to those familiar with the art of electrical signaling, and, particularly telephony, that when a potential is applied toa circuit which is paralleled by the conductors of another circuit a difference of potential may be created in the paralleling circuit, due to the proximity of the two circuits and to irregularities in one or both circuits. The current which flows in the paralleling circuit is' commonly known as crosstalk current.

It is the object of this invention tolocate the position of the cause or causes of such crosstalk, that is,todetermine the distance along the circuits from a predetermined point thereon.

This invention will be clearly understood from the following description when read in connection with the attached drawing, 01 which Figure 1 shows one form of embodiment of the invention; Figs. 2 and 3 represent diagramn'iatically certain characteristics of the'apparatus shown in Fig. 1 and Figs. 4 and 5 show variations of the invention.

In 1, L and'L represent two circuits which are so disposed geographically that crosstalk current may be set up in line L by current from the line L,. These circuits are connected with the testing circuit at the terminals 0. and Z) respectively. The object of the invention is to determine the distance 3 along the parallel circuits from the point where the testing apparatus is connected with the line circuits to the position of the source of the crosstalk.

The apparatus used is known in telephony as a transmission measuring set and the par ticular form disclosed here for the purpose of illustrating and describing the invention is that disclosed in the patent to A. 13.

Clark, No. 1,471,383, which issued on Oct.

23,1923. In Fig. 1 a source 1 of sinusoidal winding of the transformer 2, the secondariesof whlch are connected with the sides of a circuit which has bridged across it the resistances 3 and 4. The oscillator 1 may he of any well known type that may be adjusted to produce currents of predetermined frequencies throughout a predetermined range. across the resistance 3 will cause a flow of current through the primary winding of the transformer 14 when the switches Band 12 are in their normal or unoperated positions. When switch 5 is operated current will flow over the conductors of pair 7 and thence over the conductors of the line L which is connected with the testing circuit at the ter minal a The secondary windings of transformer 14 are connected with the movable arms of key or switch 8, theinside contact points of which are connected with the terminals (a of the test set and the outer contact points of which are connected with the resistance 9. In similar manner the opposite terminals of the said secondary windings of transformer 14 are connected with the movable. arms of key 10, the inner contact points of which are connected with the terminals 6 of the test set and the outer contact points of which are connected with the resistance 11, which differs in magnitude from the resistance 9. The conductors of pair 32 which are connected with the terminals 6 of the test set are also connected with the outer contact points 13 and 13 0f the switch 12. Bridged across'the midpoints. 15 and 15' of the secondary windings of transformer 14 is the pirmary winding of transformer 16, the sec ondary winding of which is connected with the artificial line 17. Bridged across what may be termed the output side of this artificial line is a potentiometer 18, which is connected with the primary winding of the transformer 19. The secondary winding of this transformer is connected with an amplifier, represented by the vacuum tube 20. This amplifier may however, be of any substantially distortionle:s type and may compri'e any number of stages anupliliratiou. The output side of this amplifier is con- The potential difference existing which are joined together and connected with two electrodes, viz, the filaments of two vacuum tubes 23 and 29 which function as rectifiers. The said resistances 24 and 27 have connected in parallel therewith condensers25 and 28 respectively. One of the conductors of pair 22 is connected with resistance 24 and the other with the grid and plate of th vacuum tube 23 which are strapped together to function as asingle electron c. The reference circuit 31 is con nectcd by transformer 30 with the resistance 2? and also with the grid and plate of the vacuum tube 29 which are strapped together. Two electrode tubes may, ofcourse, be used in place of the three electrode tubes shown. These tubes rectify thealternating currents impressed thereon by, the circuits 22- and 81 and the resulting direct currents flowing through the equal resistances 24 and 27 will, if unequal, cause a deflection of the galvanometer 26.

Another amplifier, represented by dotted lines and designated A may be inserted in the line L to amplify the crosstalk current flowing therein if it is felt that additional amplification is necessary.

The lines L and L are interconnected preferably at the point where these lines join the terminals of the test set bythe equal resistances 37, which serve to feed back from line L to L a certain amount of current in phase with the voltage of the source 1, the purpose of which will be apparent from subsequent description.

To measure thedistance tothe source of crosstalk th circuit is arranged as follows: Switch 5 i operated to close contacts 6 and (3" to bridge thecircuit 7 across the resistance 3 and switch 12 is operated to close contacts 16 and 13 to lu-idge the circuit 32 across the primary winding of transformer 14. Switches 8 and 10 are operated so asto connect the resistances 9 and 11 across the terminals of the secondary windings of transformer 14. With the switches thus arranged, the oscillator 1 is adjusted to pro duce a potential of a definite frequency which is applied across the winding of transformer so as to cause current to flow through the re istances 3 and 4, thereby set ting up potential differences across the said resistances. The potential difference across 8 will cause current to flow over the circuit 7 and the line circuit L The potential difference across the resistance 4 will cause current to flow over circuit 31, which will be impressed by the iransforn'ier 30 upon the balance indicating system. Due to the rectifying action of the vacuum tube 29 a unidirectional current will' flow over a circuit that may be traced from the filament of tube 29, conductor 33, resistance 27 in parallel with resistance 24 and galvanometer 26, the secondary winding of the transformer 30 and the plate and grid of vacuumtube 29. The grid and plate of each vacuum tub used in the balance indicating system are in efi'ect a single electrode and are intended to represent the manner in which the ordinary threeel'ement tube may be'adapted for rectifying purposes. The flow of current through the galvanometer 26 would tend to cause a deflection thereof but this'is prevented by the flow of current produced in the balance indieating.- system by circuit 22,- the manner of doing which will be made clear.

If there is some irregularity crosstalk current will be set up in the line L This current will flow over the line L tothe terminals Z), thence over the circuit 32 and through the contacts 13 and 13 to the'pri-- mary winding of the transformer 14. This current will be combined with a certain amount of current that flows from L to L over the by-pass circuit-that includes there I sista-nces 37. It should therefore begborne in mind that the current in the primary winding of transformer 14 is a combina tion of the crosstalk and of the by-passed currents, because certain subsequent efi'ects' depend upon this combination. Since-keys 8 and 10 have been operated the resistances 9 and 11, which areunequal in magnitude, will be bridge across the terminals of the other windings of transformerlt. The u'nbalanced situation existing will cause a'difference of potential across the points 15- and 15", which will cause the induced current to flow through the primary winding of transformer 16. The difference of potential established across the-secondary winding of 16 will cause current to flow through the" artificial line and through the potentiometer 18 and the magnitude of the current flowingthrough the primary winding of transformer 19 will be determined by th setting of the artificial line 17 and of the potentiometer 18. This current will be amplified by the amplifier 20 and wil be impressed by transformer 21 upon the. circuit 22. This currentwill be rectified by the tube 23 and the rectified current will flow through resista-nces 24 and 27 and through the galvanometer 26. The artificial line 17 should be adjusted until the rectifiedcu'rrent from circuit. 22 equals that from circuit 31, which will be indicated by a balanced condition'of the galvanometer 26. The reading of the artificial line is the measurement in miles of standard cable of the relation between the .jilii'l of the crosstalk current in line L and the by-pass current in resistance 37, and the current entering line L for the frequency at which the oscillator is adjusted. for this particular reading.

It will be seen that in making the measurement just described the transmission measuring set impressed a definite potential represented by the vector E in Fig. 2 upon the sending end of the disturbing line L This causes current to flow over the disturbing line through the crosstalk path and back to the transmission set by way of the disturbed line L Due to the length ofthis path and the finite velocity of propagation the current returning to the transmission set, which is represented by I of Fig. 2, will lag behind the voltage by a certain angle, such as that between I and E. If the lines L and L are completely separated from each other except at the point where the crosstalk occurs, that is to say, if there were no bridging connection such as 37 between L and L and the magnitude ofthis crosstalk current were measured, for example, in miles of standard cable at various frequencies, and a surve was plotted between frequency and miles, such curve would resemble that indicated by A of Fig. The position and slope of this curve would depend upon the properties of the lines L, and L and the nature of the crosstalk path.

In order to determine the distance :0 from the point where the measuren'ient is made to the location of the source of crosstalk a local by-pass circuit 37 effectively connecting the ends of the lines L and .L is used. The exact nature of this by-pass circuit is not material to the performance of this measurement, except that it must not produce a phase shift which varies with the frequency of the current passing through it. WVhen resistances are used, the current which passes through the by-pass circuit is in phase with the impressed voltage E. Such current is represented by the vector I in Fig. 2. The current through the local l'iy-pass circuit should be approximately equal in magnitude to the crosstalk current which reaches the transmissionmeasuring set. It has been pointed out that if the crosstalk current is small an auxiliary amplifier A represented by the dotted lines upon the circuit L may be used to increase the crosstalk current. This amplifier, however. should not contain a filter or any other device which produces an appreciable amount: of phase shift which varies with frequency. The transmission measuring set measures the resultant of the crosstalk current and the current through the by-pass circuit 37. As the frequency is varied the current in the by-pass circuit remains in phase with the applied voltage E but the current from the I cross talk circuit L varies in phase with the frequency. Consequently, at some frequenc ies the currents add up, producing a low measured transmission equivalent, and at other frequencies these currents oppose, pro ducing a relatively high measured equivalent.

It has been pointed out that the galvanometer 26 is acted upon simultaneously by a voltage due to the presence in resistance 27 of a rectified current from circuit 31, and by a voltage due to the presence in resistance 24 of a rectified current from circuit 22. By adjusting the artificial line 17, the currents in circuits 22 and 31 may be made equal and the galvanometer 26 brought to zero. If the oscillator l is operated at a plurality of frequencies throughout a definite range and the re'ading of the artificial line 17 when a balanced condition is obtained be noted for each frequency and if acurve be plotted between frequency and miles of transmission, such curve would have a series of humps, such as is shown by curve B of Fig. 3. If V and V are the ve-' locities of propagation over the lines L and L respectively and A is the frequency in terval between the humps of curve B of Fig. 3, the distance a: from the measuring apparatus tothe source of crosstalk is given by the formula f( 1+V2) In case the two circuits have the same velocity of propagation V, this formula becomes V x 2A f which is the familiar formula for locating irregularities by means of the humps in an impedance curve.

Figs. 4 and 5 represent the method for locating the causes of crosstalk in phantom circuits, namely the crosstalk which exists between the phantom circuit and one of its side circuits. In these figures the transformers T and T are of the type known in telephony as phantom repeating coils. The phantom circuit is obtained by connecting directly with the midpo-ints of theline windings of the coils T and T If there were an irregularity such as is represented by the resistance R, in one side of one of the line circuits, such irregularity would cause crosstalk between the phantom circuit and this side circuit. This side circuit is connected through the pair 34 with the amplifier A and thence with the terminals 7) of the transmission measuring set. The other terminals a of this set are connected with the midpoints of the line windings of the transformers T and T This transmission measuring set, which is the same as shown in Fig. 1, is adapted to apply a potential across the terminals a, which will between said line circuits.

cause a flow of current over the lines L and L Since there is an irregularity It existing in the line L, the currents flowing from the midpoint of the winding 35 of transformer T to the two sides of the line L, will be unequal and accordingly there will be induced in the winding 36 a potential resulting from the difference in magnitudes of these currents. This potential will cause a flow of current over circuit 34:, which cur rent is the crosstalk current. This current will be amplified by the amplifier A and impressed across the terminals Z) of the transmission measuring set.

In order to feed back a certain amount of current in phase with the potential of the testing source a resistance R is inserted in one of the conductors of the line-L shown in Fig. 4. In Fig. 5 a feed-back connection containing two equal resistances R and It, is established between the output side of the transmission measuring set and the input side of the amplifier A,. By thus feed ing. back a certain amount of the in-phase current and combining this with the crosstalk current a series of humps is created in the crosstalk curve, such as B of Fi 3, by means of which the location of the cause of crosstalk may be determined by the formula given above.

Although this invention has been disclosed as embodied in a particular form it is to be understood that it is not limited to this form but is capable of embodiment in other forms without departing from the spirit and scope of the appended claims.

WVhat is claimed is:

1. In a system for locating causes of crosstalk, the combination with a disturbing line circuit of a disturbed line circuit, the said circuits being characterized by a causeof crosstalk existing therebetwee n, a transmission measuring circuit connected with said line circuits and a bypass connection 2. In a system for locating causes of crosstalk, the combination with a disturbing line circuit of a disturbed line circuit, the said circuits being characterized by a cause of crosstalk existing therebetween, a by-pass connection between the said line circuits, a transmission measuring circuituconnected with. said line circuits arrzuiged to'measure the resultant of the crosstalk current and of the lay-passed current created in the disturbed circuit, by the by-pas'scoimectioifbetween the said line circuits.

3. In a system for locating causes of cross talk, the combination with a disturbing'line circuit of a disturbed line circuit, the said circuits being characterized by aflcause of crosstalk existing therebetween, a transmission measuring circuit connected with said line circuits having a source of sinusoidal voltage connected therewith and a by-pass connection between the said line circuits at or near thepoint of connection of the said measuring circuit to the saidline circuitsto produce a current in the disturbed circuit havinga definite phase relation to the voltage'of the said source, the measuring circuit being adapted to measure the resultant of the crosstalk current and the by-passed current. I

l. In a system for locating causes of crosstalk, the combination with a disturbing line circuit ota'disturbed line circuit, the said circuits being characterized by a cause of crosstalk existing therebetween, a transmission measuring circuit connected with the saidline circuits having means for applying a sinusoidal voltage to the said disturbing circuit, and a, by-pass connection between the said line circuits of such character as to transmit therebetween current ha-vinga constant phase relation to the applied voltage, the said measuring circuit having means to measure the resultant of the crosstalk current and the by-pass current.

5. In a system for locating causes of crosstalk, the combination with a source of sinusoidal voltageof a disturbingcircuit connectedwiththe said source and a disturbed circuit having a current setup therein by virtue of a cause of crosstalk existing between the said circuits, a by-pass connection between the said circuits of such character as g to transmit therebetween currents having a constant phase relation to the impressed voltage, and a transmission measuring circuit containing two paths, one connected with-thesa-id. disturbed circuit and the other connected with the said source, and a measuring. arrangement' connected with both 1 paths; comprising means to balance the crosstalk current comblned with the bypassed current against the sinusoidal current from the said source of voltage.

6. In a system for locating causes of cros5stalk, the combination with a source of sinusoidal .voltage of a disturbing circuit connected with the said source and a disturbed circuit having current set up therein by virtue of a cause of crosstalk existing between thes'aid circuits, a resistance by-pass connection between the said circuits at 'or near the point of connection of the said source with the said: disturbing circuit, and a trans mission measuring circuit containing two paths,-one connected with the said disturbed circuit and the other with the said source, anda measuring arrangement connected with both paths, having means to opposethe crosstalk current combinedwith the bypassed current against the sinusoidal current from the said source of voltage.

7. In a system for locating causes of crosstalk, the combination with a source of sinusoidal voltage, of a disturbing circuit connected with the said source and a disturbed circuit having current set up therein by virtue of a cause of crosstalk ezris't'ng between the said circuits, a by-pass connection between said circuits at or near the point of connection of the said source with the said disturbing circuit, the said by-pass being of such character as to transmit therebe tween current in phase with the impressed voltage, and a transmission measuring circuit having a path connected with the said disturbed circuit and another path connected with the said source, the said measuring circuit having a differential measuring device to oppose the crosstalk current combined with the by-passed current against the sinusoidal current from the said source of voltage.

8. In a system for locating causes of crosstalk, the combination with a plurality of transmission circuits having a cause of crosstalk existing therebetween, of a transmission measuring circuit having a balance indicating device connected therewith, a source of testing voltage arranged to be connected directly with one of said transmission circuits and also with said balance indicating device, a resistance by-pass connecting said source with the other of said transmission circuits, means for applying to the said transmission measuring circuit the crosstalk current combined with the by-pass current from said source, and means for simultaneously applying to the said measuring circuit other current from the said source of testing voltage.

9. In a system for locating causes of crosstalk, the combination with a plurality of transmission circuits having a cause of crosstalk existing therebetween, of a source of testing voltage, a balance indicating device, switching means for aplying the said voltage to one of said transmission circuits and to said balance indicating device, switching means for applying to the said balance indicating device the crosstalk current set up in the other of said transmission circuits combined with a predetermined amount of current in phase with the voltage from said source of testing voltage, and current controlling means to equalize the currents applied to the said balance indicating device.

10. In 'a system for locating causes of crosstalk, the combination with a plurality of transmission circuits having a cause of crosstalk existing therebetween, of a source of testing voltage connected with one of said transmission circuits, a balance indicating device connected differentially with the said source and with the other of said transmission circuits, a bypass connecting said source and said other of said transmission circuits whereby current in phase with the testing voltage may be combined with the crosstalk current, and means to equalize the currents impressed on the said balance indicating device.

11. The method of locating causes of crosstalk in an electrical transmission system comprising a plurality of parallel circuits having a cause of crosstalk existing therebetween which consists in applying a sinusoidal voltage of definite frequency to one of said circuits to produce crosstalk current in the other of said circuits, combining the said crosstalk current with sinusoidal current of definite magnitude and in phase with the said testing voltage, and measuring the transmission equivalent of the C0111- bined currents at various frequencies throughout a definite range.

In testimony whereof, we have signed our names to this specification this 21st day of December, 1923.

ALVA BENSON CLARK. GEORGE CRISSON. 

